Bearing assemblies are employed to provide a sliding or rotating movement and typically provide support and permit rotation of a rotatable shaft element with a minimum of friction. For example, bearing assemblies, such as ball- or roller-bearing assemblies, are employed to support the spindle-disk-drive shaft employed to drive a computer magnetic disk which is read by a memory head. The computer disk and memory head must be protected from an outside environment, and typically a ferrofluid exclusion seal is employed, and such ferrofluid exclusion seals are employed as a separate component. While the ferrofluid exclusion seal used, for example, with a rotating shaft, such as a computer-disk drive shaft or spindle, is satisfactory, having the seal apparatus as a separate component, is not always satisfactory, particularly where space requirements are at a minimum.
Ferrofluid seal apparatuses, such as multiple-stage seal apparatuses, have been employed in conjunction with ball bearings to support a shaft, such as, for example, set forth in U.S. Pat. No. 3,620,584, issued Nov. 16, 1971. Further, ball-bearing assemblies have been employed using a magnetic ball bearing, in order to retain ferrofluid lubricants in place, such as set forth in U.S. Pat. No. 3,977,739, issued Aug. 31, 1976.
This application is a continuation-in-part of the single-pole-piece ferrofluid seal apparatus as described in U.S. patent application Ser. No. 450,339, filed Dec. 16, 1982 (now U.S. Pat. No. 4,407,508, issued Oct. 4, 1983), which application is hereby incorporated by reference. This application describes a single-pole-piece seal apparatus having a single magnetically permeable pole piece, an annular permanent magnet, means to secure the pole piece and the magnet together, and with one end of the pole piece extending into a close relationship with the surface of the shaft to be sealed, to define a radial gap, and ferrofluid disposed in the radial gap, to provide an exclusion seal or a pressure-type seal. The magnetic flux path of the single-pole-piece seal extends through the permanent magnet, the single pole piece, the ferrofluid in the radial gap, the shaft element to be sealed and an air gap between the shaft element and the other end of the permanent magnet, with typically the radial gap being shorter or less in gap length than the air gap. The single-pole-piece ferrofluid seal apparatus is particularly useful where space is at a premium, and where the shaft comprises a small-diameter, high-speed shaft element, and with the magnetic flux concentrated in the radial gap, the magnetic flux density in the air gap being quite small.
This application is also a continuation-in-part of U.S. Ser. No. 526,781, filed Aug. 26, 1983, which discloses and claims a bearing assembly with an integrated ferrofluid seal, which bearing assembly comprises: an inner and outer race; plurality of roller elements; means to retain the roller elements within the races; and a single-stage ferrofluid seal within the raceway to provide a ferrofluid exclusion seal; for example, to prevent the passage of ferrolubricants or lubricants employed in the bearing assembly into a contamination- or environmental-free area. In the bearing assembly of the parent application, a single-stage seal is employed and comprises a pole piece and an annular permanent magnet, together with a nonmagnetic permeable housing extending about a portion of the pole piece and the permanent magnet in order to provide and act as a magnetic flux insulator so as to divert magnetic flux toward the surface of the inner or outer race in which the ferrofluid seal is formed, since the inner and outer races are typically composed of a metal, that is, a magnetic permeable material.
Therefore, it is desirable to provide a bearing assembly having an integrated, single-pole-piece ferrofluid exclusion seal, wherein which bearing assembly is compact in design and is particularly useful where space requirements are important.